The present invention relates to a coating composition, which when applied to a substrate, forms a protective, abrasion-resistant coating thereon, and which coated substrate has been found to be readily tintable. More particularly, the present invention relates to a colloidal silica coating composition employing a free radical initiator and an organic tintability additive which remains substantially unpolymerized even after the remainder of the coating composition is cured onto the substrate.
It is known in the art that colloidal silica can be included in abrasion-resistant coating compositions, also referred to as hardcoating compositions. Examples of such colloidal silica hardcoating compositions are Chung U.S. Pat. No. 4,348,462; Perkins et al. U.S. Pat. No. 5,221,560; and Perkins et al. U.S. Pat. No. 5,296,295.
Chung U.S. Pat. No. 4,348,462 discloses a colloidal silica hardcoat composition. Chung also discloses that additives, such as pigments or dyes, can be added to the composition. The present invention relates to a change in color or light transmittance brought about by adding a color additive, e.g. dye, after the composition already has been cured onto a substrate, not by adding the color additive to the coating composition before curing.
Perkins et al. U.S. Pat. Nos. 5,221,560 and 5,296,295 disclose a tintable hardcoat composition but the tintable additive in Perkins et al. is polymerized. In addition, the Perkins et al. patents refer to cationic-type initiators, used alone or in combination with a free radical initiator. The Perkins et al. patents do not disclose the use of a free radical initiator alone. The present invention, on the other hand, requires only a free radical initiator. Further, the tintability additive of this invention remains substantially unpolymerized. It has been discovered that the compositions of this invention result in improved tintability without any appreciable loss in abrasion resistance.